SERIAL COMMUNICATION

Parallel transmission: Data is sent 8 bits (byte) at a time over 8 data lines.

A few handshaking lines may be needed. One uses a 25-pin

D-shell connector and cable(DB-25 or equivalent)

Serial transmission: Data is sent one bit at a time over one data line. In theory and

principle one needs only two lines for data, one for the signal

and the other for ground. A few clock and handshaking lines

are needed and in many PCs a 9-pin connector is used.

Serial Communication TypesAsynchronous

Synchronous

Transfer:

Simplex

Half duplex

Full duplex

Asynchronous Data

Synchronous Data

UART:UART means Universal Asynchronous Receiver and Transmitter 8051 have single UARTIn LPC2148 have two UART

Serial communication in LPC2148

UART

UART0 block diagram

Pin description

UART0 pin description

Pin Type Description

RXD0 Input Serial Input. Serial receive data.

TXD0 Output Serial Output. Serial transmit data.

UART0 REGISTER MAP

U0FCR-FIFO CONTROL REG• 8-BIT Byte Addressable reg• This reg is used to enable TX & RX FIFO

functionalities

• U0FCR=0x07 is like SCON reg

U0LCR- Line Control Reg• 8-BIT byte addressable reg• Line control reg is used to select the

length of char

• LSB two bits are char length selection bits.

U0LCR=0x83 baud rateU0CLR=0x03

0 0 – 5(xxx00000)0 1 – 6(xx000000)1 0 – 7(x0000000)1 1 – 8(00000000)DLAB(Divisor Latch Buffer) one high-low pulse across DLAB bit indicates

baud rate is successfully loaded. DLAB=1 baud rate is loading DLAB=0 After loading baud rate DLAB must be

zero.

Baud rate=clk/16*9600

Divisor Latch Reg• DLR is 16-bit reg• Used to load baud rate• As the baud rate is 8-bit value, divide DLR

into two parts• DLM & DLL(8-bit each)• For 9600 baud rate • U0DLL=0x63(12mhz)• U0DLM=0x00

U0THR(Transmit hold reg)• 8-bit byte addressable reg• Data can be loading to U0THR, whenever

transmitting data• U0THR=‘A’----like SBUF• THR buffer reg is used only for

transmitting

U0RBR(UART0 Receive buffer reg)8-bit byte addressable regData can be loading into U0RBR,

whenever receiving data.a=U0RBR----like SBUF

U0LSR(UART0 line status reg)

8-bit byte addressable regConsists of diff flag bits… TI interrupt & RI

interrupt flag bit0th bit of LSR is RI flag bit6th bit of LSR is TI flag bitMonitoring TI bit syntaxWhile(!(U0LSR&0x40));Monitoring RI bit syntaxWhile(!(U0LSR&0x10));